Examples known double-structure substrates are described in Maleville et al., 2000, “Multiple SOI layers by multiple Smart Cut™ transfers”, IEEE International SOI Conference, pp 134-135. Double-structure substrates described therein comprise, in succession, a support, a first insulating layer, a first crystalline layer, a second insulating layer and a second crystalline layer.
Such double-structure substrates are useful for the fabrication of microelectronic devices, e.g. certain CMOS transistors, having high-performance but low-power consumption. In particular, multiple gate devices can be fabricated in double-structure substrates, one gate being fabricated in the buried first crystalline layer and a second gate being fabricated on top of the second crystalline layer. In such devices, electrical potentials under the gates sources, drains and channels on the top of the second crystalline layer can be controlled by appropriate operation of gates in the buried first crystalline layer.
Devices fabricated in double-structure substrates achieve high-performance and low-power by reducing the parasitic capacitances between the gates sources and drains and their supports that are typical in traditional single-structure substrates. Such devices cannot be fabricated in traditional single-structure substrates, since they do not have the second insulating layer and the second crystalline layer.
However, the cited document teaches that manufacturing such double-structure substrates is complex, requiring sequentially performing two layer-transfer operations, one layer-transfer to form the first insulating layer and first crystalline layer and the second layer-transfer to form the second insulating layer and top crystalline layer. Although high quality stacks of crystalline layers can be manufactured, their higher costs limit or prevent their economical use in lower-cost, consumer end products mobile phones, PDAs, and the like.